car boot sale 
noun British
An outdoor sale at which people sell unwanted possessions, typically from the boots of their cars.Either he's clearing a house or he's an ardent searcher on the car boot sale, jumble sale and charity shop circuits....
- It is possible someone is trying to sell them at a car boot sale or market.
- We are told it is likely that they were stolen either ‘to order’, or to be sold at a car boot sale.